AIP Advances (Apr 2014)

Built-in voltage of organic bulk heterojuction p-i-n solar cells measured by electroabsorption spectroscopy

  • E. Siebert-Henze,
  • V. G. Lyssenko,
  • J. Fischer,
  • M. Tietze,
  • R. Brueckner,
  • M. Schwarze,
  • K. Vandewal,
  • D. Ray,
  • M. Riede,
  • K. Leo

DOI
https://doi.org/10.1063/1.4873597
Journal volume & issue
Vol. 4, no. 4
pp. 047134 – 047134-10

Abstract

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We investigate the influence of the built-in voltage on the performance of organic bulk heterojuction solar cells that are based on a p-i-n structure. Electrical doping in the hole and the electron transport layer allows to tune their work function and hence to adjust the built-in voltage: Changing the doping concentration from 0.5 to 32 wt% induces a shift of the work function towards the transport levels and increases the built-in voltage. To determine the built-in voltage, we use electroabsorption spectroscopy which is based on an evaluation of the spectra caused by a change in absorption due to an electric field (Stark effect). For a model system with a bulk heterojunction of BF-DPB and C60, we show that higher doping concentrations in both the electron and the hole transport layer increase the built-in voltage, leading to an enhanced short circuit current and solar cell performance.